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BobL
30th Mar 2013, 11:11 PM
After making a few enquiries, discussions with the electrical furnace lads where I used to work, some calls to furnace suppliers, a few late nights on the internet and a few PMs with Corin I have decided to have a crack at building a natural gas fired forge.

The requirements are
- it has to be mobile as the only natural gas point we have outside the house is on the back veranda. SWMBO says I can use it there but when guests come it has to be removed at very short notice. Also a couple of other members have expressed interest in using it.
- Has to be able to anneal, harden and temper wood work tool blades up to ~10" long - it would be nice to be able to be able to go longer but that is not high on the priority at this stage
- Initially it has to be natural gas powered,
- has to be quick - can't afford to hand around waiting for heat up (OTOH that means it cannot be left unattended so lengthy heat treatments are unlikely)

So this is where I am currently at

http://www.woodworkforums.com/attachment.php?attachmentid=260579&stc=1
Yes I agree it looks like something homeland security might be knocking on my door about soon.

The trolley is all ally jobbie I fished out of the skip where I used to work. It used to support a large 1960's Storage CRO that stopped working and was thrown out years ago.

The trolley has solid lockable wheels and a drawer a nice handle to move the whole thing around even when it is hot. The handle can also be used to hook forge tools over.
The forge body is supported on steel legs 110 mm away from the trolley to improve working height and also to protect the trolley.
The space underneath will be used to locate a small blower. Because natural gas does not have much energy and is also delivered at low pressure the high temperatures needed in forges can only be obtained using force/blown torches - more about that later.

Most of the 3/4" galv plumbing pieces and pipe come from my FILs bottomless box of plumbing pieces. The 1/2" stuff comes mainly from leftovers after installing the retic compressed air in the shed. So far I guess I have spent $40 on taps and bits and pieces.

The body of the forge is based on a small LPG bottle but what I have been focussing on mainly so far is the gas and air plumbing components.
There is still a fair bit of work to do on the body like cutting the ends off and cutting doorways at either end and adding small doors and then of course lining the interior etc
AFter lining and adding a refractory brick floor there will be ~8" of working diameter and an internal working length of ~14" which I am pretty happy about.

I am also making the entire ends of the bottle into large doors on hinges so that they can be opened up to view the torch tip positions more easily, and so the lining can be more easily replaced when required.
Because the interior of the forge after lining will be ~700 cu in the recommendation is to use two torches for that volume.
Here is one of the torches
http://www.woodworkforums.com/attachment.php?attachmentid=260581&stc=1
The nozzle is 304L stainless to cope with the high temperature at the torch tip.
I can get a nice blue cone from this torch but for better flame stability the tip is supposed to be flared - something else to have a look at.
The T-piece with the wire coming away from it is a BBQ lighter point.
The chrome tap and all the flexy gas lines come from a skip outside a lab reno where I used to work and they are proper lab gas taps and hoses.
The big steel collar on the porch locks the torch to the tank and enables the height of the torch in the tank to be adjusted via a couple of grub screws

This is what the operator will see in front of them
http://www.woodworkforums.com/attachment.php?attachmentid=260583&stc=1
The yellow handle lever tap is the master gas switch.
The two taps with the yellow tops are gas flow control to each torch
The red handles on the left (yes there are two - one is behind the topmost gas tap) are air flow control to each torch.
The blue handle and red handled taps on the right are part of an idle circuit - more about that later.

Here you can better see the master gas control (yellow lever) and the idler circuit (blue and red handled taps)
http://www.woodworkforums.com/attachment.php?attachmentid=260586&stc=1

Here is a view from the other side showing the two air controls (red handled taps)
The large 25 mm brass adapters at the very top are forced air input lines - they don't have to be that big and I will probably scale then down when I sort the blower out.
http://www.woodworkforums.com/attachment.php?attachmentid=260584&stc=1

Here is a view of the torch tips inside the tank,
Bear in mind 2" of insulation need to go around the inside of the tank - the torch tips should not be protruding below the lining..
http://www.woodworkforums.com/attachment.php?attachmentid=260585&stc=1
You can also see how rusty the inside of the tank was.
The black gunk is the effect of phosphoric acid on the 1/2 mm thick layer of rust.

Nothing has been finally bolted or sealed in place. The bolts protruding into the tank will be turned around so that only their heads are inside the tank so they don; interfere with the lining.

In terms of a forced air supply I have been experimenting with a vacuum cleaner that has variable speed air flow control but even that seems to be way too much air so I had to add air flow control taps and spill most of the air during the testing with one torch - I don't expect much will change with two torches. I picked up a nice gentle blower out of a blower heater yesterday during kerbside pickup that might work - have to take a look at that more closely. Anyway -I have done enough experimentation to feel confident enough that it should work so I am working on the furnace body and plumbing first.

The build is a slow process (much slower than I thought it would be) but I am enjoying it and can't wait to make some heat.

AndrewOC
31st Mar 2013, 12:19 PM
Flash stuff Bob!
I can't wait to hear how the firing goes; looks like you'll be able to forge out of it as well as heat treat.
Tried a vacuum cleaner as a blower, just rather noisy, and as you pointed out, more than enough air. On the 6" out let blower at the Heritage Fleet I made a manifold with spigots to tap off air for heat treating (eg air hardening), extra forges and air curtains.
enjoy,
AndrewOC

cava
31st Mar 2013, 02:42 PM
Looking good. Consider getting a variable pressure regulator for the supply gas bottle as it will give you more control and a safety margin.

Consider this regulator.
LPG Regulator (http://www.auscrown.com/page/shop/flypage/product_id/80/a/category/e/hose_regulators_regulators)

BobL
31st Mar 2013, 03:19 PM
Flash stuff Bob!
I can't wait to hear how the firing goes; looks like you'll be able to forge out of it as well as heat treat.
Cheers Andrew, yeah funny how I started out by considering a 9kg gas cylinder and now I'm heading into two burner territory.


Tried a vacuum cleaner as a blower, just rather noisy, and as you pointed out, more than enough air. On the 6" out let blower at the Heritage Fleet I made a manifold with spigots to tap off air for heat treating (eg air hardening), extra forges and air curtains.
The vacuum cleaner I'm using (a council kerbside pick up jobbie) is not too bad for noise and has variable speed air flow ranging from 16 to 40 cfm (it sure is nice to have air flow measuring gear on hand to do this) but even the slowest flow is way too much. I like your idea of a manifold and air curtain, what do you use the air curtain for?


Looking good. Consider getting a variable pressure regulator for the supply gas bottle as it will give you more control and a safety margin.
Thanks for the suggestion but I'm not using LPG, I'm using natural gas ie the external gas bayonet where I hook up my BBQ. The lab gas taps provide excellent control as they have many turns.

The pressure in at the bayonet is very low (<1 psi) and there is a regulator in the flexy line connecting the bayonet to the forge - pressure after the regulator is also <1psi. I hope this is enough, hence also the need for a blower.

RayG
31st Mar 2013, 04:12 PM
Hi Bob,

Here is a quieter alternative to vacuum cleaners..

After trying a number of blowers, I eventually settled on a spa blower, extremely quiet and nice and compact.

http://www.backsaw.net/pics/FurnaceBurner.JPGhttp://www.backsaw.net/pics/SpaBlower.JPG

Speed is adjusted with a variac. the model is LDFB 450 I notice that it comes in several brands, but the model number seems to persist across the brands :)

Regards
Ray

cava
31st Mar 2013, 04:25 PM
Thanks for the suggestion but I'm not using LPG, I'm using natural gas ie the external gas bayonet where I hook up my BBQ. The lab gas taps provide excellent control as they have many turns.

The pressure in at the bayonet is very low (<1 psi) and there is a regulator in the flexy line connecting the bayonet to the forge - pressure after the regulator is also <1psi. I hope this is enough, hence also the need for a blower.

NG has circa 38-40 mJ/m3 and you will need a reasonable sized injector to get the heat you want. <1psi is very low. Don't you mean kPa?

BobL
31st Mar 2013, 11:04 PM
NG has circa 38-40 mJ/m3 and you will need a reasonable sized injector to get the heat you want. <1psi is very low. Don't you mean kPa?

Im not using any injector - I'm just running the natural gas pipe direct into the torch with flow control via the gas tap which has a 6 mm outlet. The flame control is basically done by controlling the forced air flow.

1 PSI = ~7 kpa so 1 kpa = .15 psi

I've just got myself a more sensitive pressure measuring device so I can measure the pressure more accurately - I'll do that tomorrow.

AndrewOC
31st Mar 2013, 11:11 PM
...what do you use the air curtain for?


Ahh that be secret blacksmith business!
Only joking!!
An air curtain can go around the furnace opening, it tends to keep the heat inside the furnace. This helps get your hands closer to the opening or (more importantly) slow down heat creep along a job that is half in the furnace and half outside, where you usually want a cool handle.
Mind you it probably would work best on a furnace with a chimney/ exhaust outlet.
A.

BobL
31st Mar 2013, 11:38 PM
Hi Bob,
Here is a quieter alternative to vacuum cleaners..
After trying a number of blowers, I eventually settled on a spa blower, extremely quiet and nice and compact.
Speed is adjusted with a variac. the model is LDFB 450 I notice that it comes in several brands, but the model number seems to persist across the brands :)
Cheers Ray. Thanks for the lead.
At this stage the noise from the variable speed VC on it's slowest speed does not seem too bad but I'm usually all for minimal noise.
I do have a whisper quiet blower from a fan heater that is possibly too weak.
I may stick with the VC as I an also a fan of air curtains :D.

cava
31st Mar 2013, 11:42 PM
1 PSI = ~7 kpa so 1 kpa = .15 psi

Woops. Sorry. I got the psi vs kPa back to front. :B

BobL
14th Apr 2013, 11:25 PM
I did a bit more on the forge in the last few days. I threw a coat of pot belly black on all the external bits to keep the lid on rust as much as I can.

I also installed the insulation/lining this morning - I realize this will be old hat for gas forge gurus but thought some of the woodworkers might be interested in the process if they wandered into this forum.

http://www.woodworkforums.com/attachment.php?attachmentid=263292&stc=1
Cutting up the insulation (I followed Corin's video on the process).
I wore my Triton full face respirator while handling the insulation.

Here you can see the main body and two ends ready to go back together.
The ends are on large removable pin hinges so it can all come apart for relining when required.
http://www.woodworkforums.com/attachment.php?attachmentid=263293&stc=1

Here it is all back together with the 1" thick silica brick floor. The blue colour is the liquid rigidizer which is sprayed onto the exposed fibre to stop it being damaged and fraying and then blowing around with the exhaust gasses
There is a firebrick door that covers the 8" wide opening - more pics tomorrow

http://www.woodworkforums.com/attachment.php?attachmentid=263294&stc=1

Now I have to wait for the rigidizer to dry - reassemble the torches and everything else and do a firing to fully set the rigidizer.

Cheers
Bob

BobL
15th Apr 2013, 04:39 PM
This morning I managed to find the last few bits and pieces and the rigidizer had dried so I was able to fire it up.

Here it is finally all together.
http://www.woodworkforums.com/attachment.php?attachmentid=263393&stc=1


The air supply currently comes from an 1800 W vacuum cleaner but I am still exploring quieter options.
The VC has variable air speed control and at the slow speed it draws about 3A (1HP).
The VC outlet has been covered over with a 50 mm sewage pipe and then it splits two ways
Most of the air is directed to AndrewOC's idea for an air curtain .
The air curtain exits from a frame in front of the door - the frame can also hold a piece of heat proof glass from an old kitchen oven so that the interior of the forge can be viewed without frying yourself.
http://www.woodworkforums.com/attachment.php?attachmentid=263394&stc=1

Here is a close up of the door. the counterweight is a 3kg cast lead ingot which balances the 1" thick silica brick and steel door via a SS cable - it works really well and sits wherever it is put.
If the door is left open the lead ingot gets warm but I could still move it with my bare hand.
http://www.woodworkforums.com/attachment.php?attachmentid=263395&stc=1

I haven't optimized anything (can't see the flame too well in the daytime) but after 5 minutes a 1/2" steel bar seems to be glowing quite nicely.
http://www.woodworkforums.com/attachment.php?attachmentid=263396&stc=1
http://www.woodworkforums.com/attachment.php?attachmentid=263398&stc=1


Here is a view from the back showing the pass through opening for handling long objects.
It also acts as an exhaust vent.
http://www.woodworkforums.com/attachment.php?attachmentid=263397&stc=1

I was only using the front torch but even after 15 minutes I could still touch the back of the forge shell without any problem - the front was hotter but nowhere near as hot as pot belly stove.
http://www.woodworkforums.com/attachment.php?attachmentid=263399&stc=1

BobL
15th Apr 2013, 06:49 PM
After a bit of mucking about I managed to get the second torch to fire up. It turns out the easiest way to do this is just to open up the gas and air taps to the max with the vacuum cleaner on slowest speed, and then crank up the revs on the VC to about 1/3 of max.

The two bright spots at the top signify the two torches are alight.
263442

After a couple of minutes the two hot spots from the two torches clearly show up on the floor of the forge
263444

The two torches generate about 10" of working length on a piece of metal - i'm pretty happy with that.
263443

Once the forge is fully warmed and running (about 10 minutes) it takes 2 minutes to heat up a 12 mm rod to working temp.

Running cost is about $2.80 an hour.

BobL
15th Apr 2013, 07:48 PM
I remembered I had a Thermocouple rated for 1600ºC in my shed and have spent half an hour turning the shed upside down and manage to find it. I then cranked the forge up again and got it to 1189ºC before it seemed to top out. I have not played around with the air/gas mix much (I just have them fully open with the VC on 1/3 of max revs) so maybe I can get some more out of it.

I'll let it cool down overnight and do a temp/time graph for a heat up tomorrow morning.

Sawdust Maker
15th Apr 2013, 08:28 PM
Interesting

can you do me a couple of horse shoes? :D

AndrewOC
15th Apr 2013, 10:26 PM
Looks great Bob.
The door is especially interesting- they give no end of trouble. We expect them to move and expect the brittle refractory to last.
you'' have heaps of fun with it. I've been using a Corin special this last few weekends at a friends place; did i say i love furnaces?!

Andrew.

BobL
15th Apr 2013, 11:58 PM
Looks great Bob.
The door is especially interesting- they give no end of trouble. We expect them to move and expect the brittle refractory to last.

The door is a copy of a door on an electric furnace I used a fair bit where I used to work and it worked for years for me without any problems. The door on my furnace worked well up until this evening when I noticed the frame width had expanded so that the refractory bricks (which was already a loose fit) was starting to wander out of the frame. I think I can easily fix this and then I think it will be fine. I wish I had moved the counter weight over just another cm or two as it gets fairly warm so I think I will add a length of wire to the existing cable so that the counter weight rises and falls below the level of the door way so then it won't get hot. lowering the counter weight will also make the whole this a bit more stable.


you'' have heaps of fun with it. I've been using a Corin special this last few weekends at a friends place; did i say i love furnaces?!
Andrew. I can certainly see a lot of possibilities opening up. I have to keep reminding myself that I primarily put this together for my tool making process but I can see some distractions heading my way.

I played around with the flame this evening and realized I do not have enough air going to the torches to blow them out so they could probably use more air.

Here is night time pick of the torch flames
263500

BobL
31st May 2013, 12:12 AM
Still waiting for a bit of time to put in my gas line to my shed but mean time I decide to pimp my Anvil stump.

I added a tool rack and some levelling legs.
Not many tools as you can see because I will be making my own.
The legs only level the stump on the concrete floor - the majority of the weight is still taken direct by the stump, the legs just stop the stump from rocking
http://www.woodworkforums.com/attachment.php?attachmentid=270257&stc=1

http://www.woodworkforums.com/attachment.php?attachmentid=270256&stc=1

BobL
25th Jun 2013, 12:08 AM
I finally got some dedicated me time and last week I installed 22 m of 19 mm diam copper underground to the shed which was a bit of a drama in itself (http://www.woodworkforums.com/f245/bobls-shed-fit-134670/index23.html#post1663804). So I can now run my forge inside my shed. I have also upgraded my fume hood ventilation to a i300 cfm unit so that I won't gas myself.

In the mean time I modified the forge gas plumbing to make it 19 mm plumbing all the way from the meter to the T piece on the forge where the gas line switches to 1/2" diam plumbing to each torch. The previous arrangement was all over the place. 19 mm to within about 2m of the back veranda gas bayonet, then 1/2" to the bayonet, the a 10 mm flexi hose to the forge, the to a 1/2" T piece and finally through gas taps with a 7.2 mm orifice so the net effect was I was gas flow limited. The other reason for going 19mm was that my gas supply is very low pressure and 22m of line could serious slow down the flow rate.

Nothing much to see really, I took away the idler circuit because it wasn't working properly and I need to rejig it.
The electronics on the gas supply post is a new starter. Previously I had a push button BBQ starter but I have switched that for a battery powered starter from a hot water system - more details below.
Anyway I fired it up briefly and got to 1100ºC with just one torch and the gas valve opened about 3/4 of the way so still have a lot to play with.
http://www.woodworkforums.com/attachment.php?attachmentid=274098&stc=1

Here is a close up of the starter. The HV unit from the HWS has a number of sensor inputs which are basically relays that can be short circuited except for one that is wired to a switch.
Throwing the switch sends a fat spark across the spark unit with a frequency of about 2 sparks per second so it lights a bit more assuredly than the push button BBQ starter.
http://www.woodworkforums.com/attachment.php?attachmentid=274099&stc=1

I heated up and belted around a bit of hot metal but it was 8:30 pm so I could not go for long.

BobL
25th Jun 2013, 08:49 PM
Haven't had time to experiment much today but I discovered a couple of things.

1) Don't disconnect an air hose for one torch back back at at the blower when the forge is running on the other torch. The hot exhaust gasses inside the forge will go back down the unconnected air hose and melt it very quickly! It's OK not to be running the torch but the air hose must be connected and blocked off. I was wondering what the hot plasticky smell was :rolleyes:

2) Make sure the air hoses are firmly connected. If an air hose comes off when the forge is at full operating gas/air the reduction in air flow to the torch generates a huge yellow flame out of the forge doorway. Before this happened I had just jammed the hoses onto their respective fitting but since then I have clamped them down firmly with hose clamps.

3) I lit the second burner and without much tuning I got the temp of a bit of steel up to 1250ºC as measured by a pyrometer. Two burners puts out a fair bit of exhaust heat and heated the whole shed up very quickly. I wondered why the ventilation fan was not coping and then realized I had the shed doors closed - it cooled a little once I opened the main shed door but its not good for the neighbours to hear me belting steel - guess it's going to be a daytime only operation.

If this sounds a bit nerve wracking - it is a little.
One certainly has to concentrate and not take things for granted - I certainly wouldn't be doing this without good ventilation.
Just for the record I also do have two fire extinguishers on hand.

pmcgee
26th Jun 2013, 07:40 PM
Bob - I'm sure you will be perfectly fine - muscled, bare-chested and sweating ... hammering away lit only in the light of a roaring furnace and the occasional solar flare.

If you did it in slo-mo it'd be like the blacksmithing version of Baywatch (complete with explosions)

... "SmithWatch" ? "Forgery" ? "Irony" ? "Hot Metal" ? "Striker & Hardy" ??

Do we now have to refer to you as 'Smitty'? :D

Cheers,
Paul

BobL
26th Jun 2013, 08:41 PM
Bob - I'm sure you will be perfectly fine - muscled, bare-chested and sweating ... hammering away lit only in the light of a roaring furnace and the occasional solar flare.
If you did it in slo-mo it'd be like the blacksmithing version of Baywatch (complete with explosions)
... "SmithWatch" ? "Forgery" ? "Irony" ? "Hot Metal" ? "Striker & Hardy" ??
Do we now have to refer to you as 'Smitty'? :D
Cheers,
Paul

Sweating - definitely, muscled -hardly :D, swearing - you bet . . . . .. I'll be taking a lot of shortcuts and my grinders and linshier will be working overtime to correct my mistakes.


Do we now have to refer to you as 'Smitty'?

FWIW my Italian grandad on my mums side was a blacksmith - her maiden can loosely be translated into smithy.

BobL
1st Jul 2013, 11:24 PM
I haven't done anything with the forge because I was waiting for a kosher 19 mm gas hose to arrive.
It looks like a fire hose compared to the standard 1/2" hose
http://www.woodworkforums.com/attachment.php?attachmentid=275227&stc=1
Now I just need to get a couple of fittings and I'll be all set.

BobL
20th Oct 2013, 12:06 AM
One of the reasons I have not done anything for a while with my forge is because I realized it badly needed some safety features.

The major problem was that being a blown gas forge, if for whatever reason the forced air supply was to stop, the small blue blown flame would immediately turn into a very large yellow fireball.
The fireball would be so big it would engulf the forge and I could not hope to get near the manual gas taps either on the forge itself or the stopcock on the wall behind the forge. Then I would have to run some 20m to the next stopcock back up near the house.

The air flow could stop for any number of reasons e.g. blower failure, mains power failure or I could just put a red hot piece of metal through one of the plastic air supply hoses.

After much mucking about, this is what I came up with to automatically turn off the gas on air flow failure.

It all starts with the psuedo Pitot tube.
One copper tube points into the air stream and the other is perpendicular to the air stream which generates a small but measurable pressure differential under air flow
290099

The pitot tube is mounted in a 3/4" BSP T fitting so that the ends of the copper tubes are in the middle of the air stream passing through the forge torch
290100

The pitot tubes are connected to this air flow switch ($20 from fleabay) using 2 pieces of black irrigation tubing - sorry its so hard to seeing being all black
The two blue taps are air pressure bypass monitors that I can attach to an air pressure meter to set the switch triggering point.
The switch is adjustable from 0.1 to 10" of WC.
290095

I have set it so that when the air pressure falls below about 0.2" of WC the air flow switch opens removing power from this 24V solenoid valve.
290101
Interestingly got the solenoid valve out of a skip at work. The valve was part of a water cooling control panel for a vacuum furnace. Tis indeed amazing what is thrown out.
The fancy looking ex-CPU fan and heat sink have been added to cool the solenoid which gets quite hot as it really meant for use use with water which would carry the solenoid heat away.

Unfortunately nothing is quite as simple as what I have described above as lighting the flame requires no forced air but some gas, so the air flow sensor needs to be temporarily bypassed while the flame is being lit.
So I made up this control box (grey box in middle of photo) that has a few bells and whistles to enable a safety aware startup to take place
290098
A small switch temporarily bypasses the the airflow sensor. At the same time the bypass displays a red LED and sounds a piezo buzzer to warn the operator that the airflow switch has been bypassed.
The operator can then manually open the gas line just a whisker to light the gas (this generates a yellow smokey flame about 150 mm long)
The the air supply is turned on just enough to get the flame approaching a green colour.
Then the gas is turned up some more, the air some more, and this is repeated until a satisfactory flame is generated.
At this point the air flow is sufficient to keep the air flow switch closed so the bypass switch can be turned off.
This also switches off the red LED and the buzzer, and also switches on an orange LED
If the power fails at anytime during start up the solenoid will still active and turn the gas off and the orange.

The control box contains the 240/24V AC transformer and the rectification circuits for the LEDs and Buzzer.

I can't use the forge for blacksmithing for another 4 or so weeks due to some surgery I had a recently but I will at least fire it up tomorrow and do some testing with small flames :oo:.

I also got myself a CO and mains gas sensor/alarm so that I don't gas myself in the process.

BobL
23rd Oct 2013, 06:19 PM
I finally fired up the forge with the new safety features and the upgraded plumbing.


The safety cut outs all work fine which I am very happy about.


Previously my gas plumbing was a bit of a mess with some section of the plumbing as narrow as 5/16" in diam.

Now I have 3/4" pipe all the way from the main line to where the gas line splits into 2 x 1/2" pipes to each of the torches.

I only measured the gas consumption for the front torch and it consumes nearly the same as the two torches together did previously.



I'm still working out optimum settings but it got a piece of metal up to 1200ºC using just the front torch and then my pyrometer started playing up so I couldn't measure any higher than this

It must have got quite a bit hotter because the forge doorway surround started to glowed hot.


I had some minor surgery a couple of weeks ago but I'm not allowed to lift anything heavier than 5 lb or engage in anything strenuous for another 3 weeks!

DSEL74
6th Oct 2014, 10:07 AM
How is the forge holding up 12mths on?

Has it had much use?

What was the gas tank that you started with? It looks like it is gal plated. Does it get hot as gal off gases toxic fumes I'm told.

Enjoyed the read thanks for sharing.

BobL
6th Oct 2014, 11:07 AM
How is the forge holding up 12mths on?
Has it had much use?

I still haven't done much blacksmithing with it (too many distractions like mens sheds and playing with motors & VFDs). I've used it mainly to heat pieces of steel so I could bend them, and heat treated a few bits of tool steel.
Another reason for this is my shed is too small and crowded for the radiant heat out put of this forge. In summer/autumn I can't use it for more than about 30 minutes because even with significant forced ventilation of my shed the forge heats up the whole shed to over 50º. Cool down time is outside air temp dependent but on a hot day it takes couple of hours to reach outside air temp. If it's 40º outside I really can't use it at all. On a cold winters day I can run for about a hour or so - cool down time is also much quicker, so I can use it 3-4 times during a cold winters day.
I did not use enough rigidizer so the insulation needs some repair. The white silica bricks are a bit fragile and can't handle repeated heating/cooling so I should find something more robust. I should probably reline it and use more rigidizer.


What was the gas tank that you started with? It looks like it is gal plated. Does it get hot as gal off gases toxic fumes I'm told.
It was a galvanised tank, from a fork lift. I was not worried about welding the galv as I have a well ventilated (2600 cfm) welding booth. Some galv around the opening did oxidise slowly during the initial couple of firings but I run the forge next to the welding booth so any fumes are very quickly ventilated out of the shed. The bulk of the tank does not get that hot so the galv is still intact.

DSEL74
6th Oct 2014, 12:35 PM
I still haven't done much blacksmithing with it (too many distractions like mens sheds and playing with motors & VFDs). I've used it mainly to heat pieces of steel so I could bend them, and heat treated a few bits of tool steel.
Another reason for this is my shed is too small and crowded for the radiant heat out put of this forge. In summer/autumn I can't use it for more than about 30 minutes because even with significant forced ventilation of my shed the forge heats up the whole shed to over 50º. Cool down time is outside air temp dependent but on a hot day it takes couple of hours to reach outside air temp. If it's 40º outside I really can't use it at all. On a cold winters day I can run for about a hour or so - cool down time is also much quicker, so I can use it 3-4 times during a cold winters day.
I did not use enough rigidizer so the insulation needs some repair. The white silica bricks are a bit fragile and can't handle repeated heating/cooling so I should find something more robust. I should probably reline it and use more rigidizer.


It was a galvanised tank, from a fork lift. I was not worried about welding the galv as I have a well ventilated (2600 cfm) welding booth. Some galv around the opening did oxidise slowly during the initial couple of firings but I run the forge next to the welding booth so any fumes are very quickly ventilated out of the shed. The bulk of the tank does not get that hot so the galv is still intact.

Thanks for the update.

I was wondering not just about the welding but the Gal in use. I have been warned off using any gal components even gal pipes for air supply on in building my coke/coal forge due to the off gassing when heated.

You could cover the the base with refractory cement. If you plan to forge weld the flux tends to damage it though.

BobL
6th Oct 2014, 03:38 PM
Thanks for the update.
I was wondering not just about the welding but the Gal in use. I have been warned off using any gal components even gal pipes for air supply on in building my coke/coal forge due to the off gassing when heated.

There is a general misunderstanding of the toxicity of the fumes coming from Heated Galv in that most people think it is highly poisonous at any level which is just not so.

Not many people realise that particularly urban dwellers already live is a soup of the same Zinc Oxide (ZnO) fumes which is present all around us from dust sources such as soil, Zn paint, corroding galvanised roofs and combustion products. The crucial difference is the concentration. These ongoing sources are always there but demonstrate that low level exposures don't have any long term health effects. Its only when the concentration gets too high that it starts affecting human health.

After it has been fired a couple of times the Galv components used on a basic coal forge would simply not generate ZnO at a fast enough rate to lead to health problems.

If you are at all worried about it, the way I would deal with it after a forge has been made would be to maximise shed ventilation, light the forge and walk away. come back every few minutes or so to add more fuel and let the forge get nice and hot. This will burn away the great majority of the galv that is likely to generate fumes. The subsequent amount of ZnO generate from running the forge will be tiny and just contribute to the general background of ZnO. The ventilation you should be providing for the forge and your self for any CO2 fumes should be more than sufficient to carry the small amount of ZnO away.

This is not correct when welding or plasma/oxy cutting galv when a large pulse of ZnO is injected into the air around the operator and it can literally take your breath away. I have done this a couple of times so I am well aware of the effects and is why I installed a well ventilated welding booth in my shed.

It's interesting to note that in terms of long term exposure the maximum recommended concentration of ZnO in air is 3 to 25 times higher than sawdust. Yet I see people squawking like headless chickens and wetting their pants over ZnO, but don't care if they are swimming in a shed full of sawdust.


You could cover the the base with refractory cement. If you plan to forge weld the flux tends to damage it though.
Yes I have thought of that

AndrewOC
8th Oct 2014, 10:39 PM
Bob
Thankyou thankyou thankyou for that most clear perspective setting of The Zinc Issue!
There has been much flapping about how murderous zinc is, with poor evidence in support. Often from fag sucking, gun toting, boozers (i.e. hypocrites).
At work tomorrow I'll ask the Librarians for the research. What stuff have you come across? I would love to share it on other forums.
A.

BobL
9th Oct 2014, 01:23 AM
Bob
Thankyou thankyou thankyou for that most clear perspective setting of The Zinc Issue!
There has been much flapping about how murderous zinc is, with poor evidence in support. Often from fag sucking, gun toting, boozers (i.e. hypocrites).
At work tomorrow I'll ask the Librarians for the research. What stuff have you come across? I would love to share it on other forums.
A.

I agree, it's kinda sad how paranoia seems to be rife about stuff that is manageable while things we should have paid attention to like smoking has taken centuries to get people to think about.
In someways it's understandable how fear of the unknown leads to exaggeration and a few rounds of Chinese whispers later and it's more dangerous than ebola.
High concentration ZnO fumes have an immediate effect which causes those exposed to sit up and immediately take notice.
ZnO effects are unfortunately tangled up with the the effects from more toxic metals like Cd and Cr which can do things directly.
ZnO exposure apparently does not kill directly but increases the chance of getting other pulmonary diseases like pneumonia.

BTW definitely be careful with old Zn compared to new Zn as old Zm has more Cd in it. It was not until the 1960s that Zn processing was changed to better remove the Cd from it.

I've worked with just about every element on the periodic table during (including some pretty toxic and radioactive materials) during my working life as a research scientist and I on a scale of 1 (least dangerous) to 10 (most dangerous) I would put ZnO is the less than 5/10 category.

I do know what it's like to have my breath taken away by fumes from welding galv which is why I put certain things like ventilation in place in my shed.
Of course I don't advocate welding the stuff willy nilly but the problem basically becomes a non-issue just by using a decent high flow extractor and if you happen to get a faint whiff or two every now and then it will not kill you.

BobL
26th Jul 2015, 10:29 PM
I haven't fired up the furnace for nearly 12 months and finally an excuse to do this came up via the mens shed where one of the guys was interested in making a couple pf practice knives from old files.

He had tried to soften the files using an oxy but all he succeeded in doing was bending one of the files. Then he tried to straighten it on an anvil and the file shattered indicating that the oxy was nit getting them hot enough for long enough. At this point I offered to soften them in my gas furnace.

5 minutes to warn up, 10 minutes at~!1150º then the gas was turned off and they were left to cool down inside the furnace.
There was still a faint visible red glow coming from the gaps around the furnace door after 30 minutes and 2 hours later the blanks were still around 300º, 3 hours after that they were 80º and I pull them out.

One of the blanks (the one directly under the torch, was bent but it straightened easily and a file was easily able to remove metal indicating they had well and truly been softened.
They look pretty manky but the scale layer is quite thin.

Now lets see what he can do with them.

http://www.woodworkforums.com/attachment.php?attachmentid=353918&stc=1

BobL
30th Jul 2015, 11:40 PM
I had the opportunity to acquire this some months ago from a relative of a member and have just got around to tidying it up

I took some photos of it when I first got it in all it's rusty glory, but now I cannot find them.

Anyway here it is after a quick once over with a wire brush on an angle grinder and the first coat of tannic acid.
It's probably going to need a half dozen coats to arrest the rust.
You can see that from the state of the rust inside the die holes.

http://www.woodworkforums.com/attachment.php?attachmentid=354390&stc=1

An here it is after its second coat of tannic just applied.
http://www.woodworkforums.com/attachment.php?attachmentid=354389&stc=1

DSEL74
31st Jul 2015, 09:56 AM
Nice swage block. I hope you put it to good use.

BobL
7th Aug 2015, 08:55 PM
Mel from the men's shed who is doing the knives did some more work on them today.

He could use a machine to form up the main bevel but he saw this bevel forming jig on the web and wanted to try it out.

That's a pretty ordinary and well used file he's using but it seems to be fair hogging out the metal so it looks like the annealing process has worked really well.

http://www.woodworkforums.com/attachment.php?attachmentid=355573&stc=1

http://www.woodworkforums.com/attachment.php?attachmentid=355572&stc=1

http://www.woodworkforums.com/attachment.php?attachmentid=355570&stc=1

http://www.woodworkforums.com/attachment.php?attachmentid=355571&stc=1

wheelinround
7th Aug 2015, 11:10 PM
an excellent build Bob :2tsup:

BobL
8th Aug 2015, 05:12 PM
Nice cold day today in Perth so time to fire up the forge/furnace again.

One of the other blokes at the mens shed had a small 100 x 250 mm (16kg) steel billet that he wanted to turn on a metal work lathe but it turned out to be hard as . . . . . . so I offered to anneal it for him.

This is by far the biggest/heaviest piece of steel I have put into the forge.

Heat up time to get to 1000 was about 15 minutes and then it took another 15 to get to 1180ºC .
The temperatures are measured by an optical pyrometer targeting the cooler outer end of the block.
On the picture it doesn't look anywhere near that temperature but that is caused be a couple of things
- by the time I open the door and futz about with the camera the end of the billet starts to cool off
- another issue is that the camera cannot handle the dynamic range of light intensity and what it means is that the bright yellow bits are much hotter.
Photos are taken using a tripod from about 3m away because of heat
http://www.woodworkforums.com/attachment.php?attachmentid=355618&stc=1

After 5 minute os so at that temp the walls of the furnace near the door which are not insulated start to glow red
http://www.woodworkforums.com/attachment.php?attachmentid=355617&stc=1

At this point I backed off the gas and reduce the temperature to 1080ºC and held that for 30 minutes.

Now the flame is not so hot and I preset up the camera on a tripod and whipped the door open and took the photo before the end of the billet started to cool off.
Now you can see the whole billet.
Notice how the lower fire brick door has cracked.
This is probably the 30th or so time the furnace has been run so I guess that's not too bad.
I have plenty of bricks and will have to remake the door and improve the frame so it will hold a cracked brick for when that happens again which is inevitable

http://www.woodworkforums.com/attachment.php?attachmentid=355616&stc=1

For the first time the CO sensor alarm went off - had the shed door closed - opening the door allowed the ventilation fan to clear the shed in a couple of minutes.

Here is the cooling curve for the billet.
I would have liked it to be a bit slower
its similar to that for the knife blanks indicating that it's the furnace itself that dominates the cooling - cracked door probably doesn't help much either.

One possibility was to put it in a box full of lime - one problem is not having anything to pick up a 16 kg lump of steel at 1080ºC

http://www.woodworkforums.com/attachment.php?attachmentid=355619&stc=1

DaveTTC
8th Aug 2015, 06:30 PM
You never cease to amaze me bob

I could use one of them furnaces atm. It must have a good impact on temps in the cave ;) brass monkey weather here atm

Dave TTC
Turning Wood Into Art

BobL
8th Aug 2015, 06:46 PM
You never cease to amaze me bob
I could use one of them furnaces atm. It must have a good impact on temps in the cave ;) brass monkey weather here atm
Dave TTC
Turning Wood Into Art


It sure does help warm up the man cave.
The furnace can generate ~22kW of energy and that has to go somewhere!
When it's cold there's a temptation to not vent any of the exhaust but it's essential to do so.
I have the welding booth exhaust running at 1200 CFM and the dusty running at 1200 CFM - I have another exhaust fan but I didn't need that today as it was pretty cold here - well for Perth anyway.
Outside it reached 15 but the temp in the man cave got up to nice 25.

eskimo
10th Aug 2015, 02:29 PM
The furnace can generate ~22kW of energy and that has to go somewhere!
.


22kw...ruddy hell my radiant gas heater (5 panel) only does about 14kw and thats nice...but the running costs ...well she just screams n screams until summer....one she wont stop cos I do have plans to put in an aircon unit.

am waiting to see the end product also...so make sure you get some pics when they are finished

BobL
10th Aug 2015, 02:58 PM
22kw...ruddy hell my radiant gas heater (5 panel) only does about 14kw and thats nice...but the running costs ...well she just screams n screams until summer....one she wont stop cos I do have plans to put in an aircon unit.

Running cost is about $3/hour but unlike a heater I don't usually have it running for very long. About the most I have had it running continuously is 90 minutes. Unlike a charcoal setup it's easy to turn it off and on although of course warm up time is still required but if it' has been off for no more than half an hour it warms up really quickly.


am waiting to see the end product also...so make sure you get some pics when they are finished
Will do.

Grahame Collins
19th Aug 2015, 02:41 PM
Very impressed- nice job Bob.

BobL
19th Aug 2015, 03:07 PM
Very impressed- nice job Bob.

Thanks Graeme,

I did some more annealing on the weekend.
I have been buying scrap steel discs from the local steel merchant ranging in size from 3 to 18 mm thick and 50 to 400 mm in diameter.
It's the same stuff I used to make the base and turntable for my ti-grinder.
http://www.woodworkforums.com/attachment.php?attachmentid=207613&stc=1&d=1336307227

The discs are obviously cut with some sort of plasma cutter so the edges are very hard and make mincemeat out of HSS.
Besides this, these discs were way too big for my little Hercus so I took them to work and turned them on the big Nutall with carbide tooling.
It's not just the edges that are hard this stuff is way harder than mild steel so drilling and tapping was a PITA and I remember breaking three 3/16" taps mounting those turntable bearings.
Young Ron from the Mens Shed (he is 85 years old) reckons it's some king of Bisalloy plate
Last weekend I decided to make something from one of the 150mm discs but knowing how hard they were I decided to see if they could be annealed.
They just fit inside the forge and yes they did get a lot softer.

BobL
24th Sep 2015, 04:45 PM
Mel from the Mens shed gave me his completed knife blanks for hardening a week or so ago and I have been waiting for a cool day to do this. Yesterday it was quite warn so I decided to beef up the shed ventilation so that I could do use my forge on warmer days.

Up until now I have been only using the forge when the outside air temp was less than 20ºC and even then for only about a hour as the shed temp would over that time build up to ~25º above the outside air temp. If I was to go longer it would get even hotter

The main problem has been the welding booth fume hood fan does not capture all the hot air and gases coming out of the forge. These hot gasses rise and accumulate in the roof space above the fume hood level of the shed and re-radiate heat back into the rest of the shed making the whole shed hot. The fume hood fan moves a lot of air but it is mostly the cool cross breeze coming in at around waste height from the door. I could really feel a temperature gradient just putting my hands above my head.

I have another squirrel cage fan at the highest part of the ceiling but the opening to the outside was quite small so all I did was increased the size of that opening. It sounds easy but it required cutting safety glass windows (made from and old shower screen) located in the roof peak. This fan has a small VFD which means I can crank the speed up a bit more than 50Hz - this moves a lot of air provided the opening is big enough ANS it removes it at max roof height so it really clears the hot gas from the shed.

Today is also a warm day so I thought I would try out the improved setup and it seems to be working. The temperature difference now seems to reach a max of around 8º AND the CO alarm does not go off whereas before it would sometimes go off.

A few pics.

Small rack for the knife blanks
358589

Cooking with gas
358590

Close up of previous
358591

Quench tank made by Mel from a piece of 4" black pipe
358594

Oils scale
358592

Top blade has be run past a Scotchbrite wheel
I'm pretty pleased with the way reducing the amount of air to the torch and heating the blades inside a large (100mm) SHS tube reduced the amount of scale
358593

DSEL74
24th Sep 2015, 10:11 PM
Bob, Did your little SHS cage just reduce scale or does it also help with an even heat to the blades?


I know the knife guys wrap their blades in S/Steel foil to keep the scale at bay.

BobL
24th Sep 2015, 10:40 PM
Bob, Did your little SHS cage just reduce scale or does it also help with an even heat to the blades?
Yes, it does both.


I know the knife guys wrap their blades in S/Steel foil to keep the scale at bay.
I was going to do that but tried the SHS cage out on a piece of scrap and it worked well so I used it in the knife blades.

Zsteve
11th Oct 2015, 09:56 PM
Hi Bob, just wondering if you still use the thermo couple or the pyrometer now?

Was thinking it would be useful to have my thermocouple inserted in my gas forge somehow. Might be able to insert mine in a small gap near the door for the times I actually need it. I guess I could drill a smal hole in the forge she'll for longer term use. how was your installed?

BobL
11th Oct 2015, 11:20 PM
Hi Bob, just wondering if you still use the thermo couple or the pyrometer now?

Was thinking it would be useful to have my thermocouple inserted in my gas forge somehow. Might be able to insert mine in a small gap near the door for the times I actually need it. I guess I could drill a smal hole in the forge she'll for longer term use. how was your installed?

I'm still using the pyrometer as I can easily target any spot I can see inside the forge.
The disadvantage of course is I can't measure it with the door closed.

BobL
27th Nov 2015, 09:17 PM
My Friend Mel from the Mens Shed finally finished his knives some time ago but I was only able to take photo of one of the finished products today when be brought a knife in to show the Mens Shed members.

359736


Here's the pouch made for it by another Mens Shed Member
359737